Merge branch 'develop' of https://github.com/1sters/material_design_zh into develop
添加封面
Merge pull request #14 from IceskYsl/master

添加封面
修改规范
修改规范
目录结构
添加常见问题
完善第一页信息
为所有模块添加图片文件夹
Merge pull request #15 from IceskYsl/master

添加常见问题
Merge pull request #16 from vincent4j/master

为所有模块添加图片文件夹
完善视频插入规范
翻译第一节
Merge pull request #17 from IceskYsl/master

翻译第一节
修改进度
renPrinciples
Merge pull request #18 from vincent4j/master

认领：Principles
认领：Principles
Merge pull request #19 from vincent4j/master

认领：Principles
translated responsive interaction chapter